The present invention relates to a novel ethylene/polyalkyleneglycol(ether) (meth)acrylic ester copolymer and a nonporous yet breathable film obtained therefrom.
Numerous nonporous yet breathable films are known; nevertheless they have poor permeability properties and poor mechanical strength. Moreover, most of these films are expensive.
There is thus a need for nonporous breathable films having improved permeability to gases, and of which the other properties are satisfactory, notably when the films are thin.
European patent application 0,538,033 discloses films which are copolymers of ethylene and hydroxy acrylate, the latter representing from 7 to 30% by weight. The hydroxy acrylate is for example hydroxyethylmethacrylate (HEMA). This polymer can be obtained in the form of films, and it is indicated that such films can be employed in applications requiring good water vapor permeability. However, the values for water vapor permeability given in the examples are relatively low, i.e. distinctly below the permeability needed for a nonporous yet breathable film application.
U.S. Pat. No. 3,494,904 discloses copolymers that are obtained from ethylene and esters of (meth)acrylic acid and polyalkyleneglycol ether. In these copolymers, the polyalkyleneglycol ether comprises an alkylenoxy group containing 2 or 3 carbon atoms, and a terminal alkoxy group comprising 1 to 4 carbon atoms. The copolymers are for example obtained by radical catalysis carried out in an autoclave. In these copolymers, the ester monomer of polyalkyleneglycol ether represents from 1 to 37% by weight. The copolymers have a mean molecular weight comprised between 20,000 and 65,000 and are used as such for heat-shrinkable films. There is no mention of water vapor permeability of such films.
JP-A-61042517 discloses an additive for improving the flow point of fuel oil, this additive being a copolymer of ethylene, of butene and polyalkyleneglycol (meth)acrylic ester, the latter making up from 1 to 200% by weight of the final polymer. These copolymers have a mean molecular weight of about 2,500, meaning that such polymers are not suitable for transformation into films.
None of these documents teaches nonporous breathable film, in other words film which is permeable to water vapor but impermeable to water, based on an ethylene/polyalkyleneglycol (ether) (meth)acrylate copolymer. None of these documents thus either teaches or suggests the present invention.